The Army's Redstone-based proposal would likely be first ready for a first satellite launch. Its connection with German-born scientist Wernher von Braun, however, was a public relations risk.[2] In any case, the Atlas and Redstone ballistic missiles were top-priority military projects, which were not to be slowed by pursuing a secondary space launch mission. Vanguard was a project of the Naval Research Laboratory (NRL), which was regarded more as a scientific than a military organization. This helped to emphasize the non-military goals of the satellite program. This was considered important, because a discussion of whether overflights of foreign countries by satellites were legal or illegal was to be avoided.

In August or September 1955, the DOD Committee on Special Capabilities chose the NRL proposal, named Vanguard, for the IGY project. The Martin company, which had also built the Viking, became prime contractor for the launch vehicle.[3] The Vanguard rocket was designed as a three-stage vehicle. The first stage was a General Electric X-405 liquid-fueled engine (designated XLR50-GE-2 by the Navy), derived from the engine of the RTV-N-12a Viking. The second stage was the Aerojet General AJ10-37 (XLR52-AJ-2) liquid-fueled engine, a variant of the engine in the RTV-N-10 Aerobee. Finally, the third stage was a solid-propellant rocket motor. All three-stage Vanguard flights except the last one used a motor built by the Grand Central Rocket Company. Vanguard had no fins, and the first and second stages were steered by gimbaled engines. The second stage also housed the vehicle's telemetry system, the inertial guidance system and the autopilot. The third stage was spin stabilized, the spin being imparted by a turntable on the second stage before separation.

The first two flights of the Vanguard program, designated Test Vehicle (TV)-0 and -1, were actually the last two remaining RTV-N-12a Viking rockets. TV-0, launched on December 8, 1956, primarily tested new telemetry systems, while TV-1 on May 1, 1957 was a two-stage vehicle testing separation and ignition of the solid-fueled upper stage of Vanguard. TV-2, launched on October 23, 1957 after several abortive attempts, was the first real Vanguard rocket. The second and third stages were inert, but the flight successfully tested first/second-stage separation and spin-up of the third stage. However, by that time, the Soviet Union had already placed the "Sputnik" satellite into orbit, and therefore project Vanguard was more or less forced to launch its own satellite as soon as possible. Therefore, a very small experimental satellite (called the "grapefruit" and weighing only 1.8 kg (4 lb)) was added to TV-3, which was to be the first test of an all-up Vanguard rocket. Although the NRL and Martin tried to emphasize that the TV-3 mission was a pure test flight (and one with several "firsts"), everyone else saw it as the first satellite launch of the Western world, billed as "America's answer to Sputnik". Wernher von Braun angrily said about the Sputnik launch: "We knew they were going to do it. Vanguard will never make it. We have the hardware on the shelf. We can put up a satellite in 60 days".[4]

On 6 December the US Navy launched a Vanguard rocket, carrying a 1.3 kg (2.9 lbs) satellite, from Cape Canaveral. It only reached an altitude of 1.2 meters (4 ft), fell and exploded. The satellite was blasted off the top of the rocket where it landed in bushes near the pad and began transmitting signals, leading to New York Journal-American columnist Dorothy Kilgallen remarking "Why doesn't somebody go out there, find it, and shoot it?" The American press called it Kaputnik.[5]

After the failure of TV-3, the backup vehicle, TV-3BU (BU=Backup), was prepared for another attempt. Pad crews hastened to repair the damage done to LC-18A by TV-3's explosion and in the third week of January 1958, the job was completed. TV-3BU was erected on the pad, but continuous delays frustrated the launch attempt. Heavy rains shorted some electrical cables on the ground and necessitated their replacement. The second stage engine was found to have damage and had to be taken down and replaced by a different stage. Finally, the launch got under way on February 5. The Vanguard lifted smoothly into the air and all appeared well until a little under a minute into the flight when the guidance system sent erroneous commands that caused the booster to pitch down. The second stage broke in half, after which the range safety officer sent the destruct signal. On March 17, TV-4 finally succeeded in orbiting the Vanguard 3 satellite. By that time, however, the Army's Juno (Jupiter-C) had already launched the United States' first satellite. The TV-4 satellite, labeled Vanguard 1, reached a relatively high orbit (3966 km (2465 miles) x 653 km (406 mi)) and is currently the oldest human artifact in space. The following four flights, TV-5 and SLV (Satellite Launch Vehicle)-1 through -3 all failed, but on February 17, 1959, SLV-4 launched Vanguard 2 (weighing 10.8 kg (23.7 lb)) into orbit. The SLVs were the "production" Vanguard rockets. SLV-5 and -6 also failed, but the final flight on September 18, 1959 successfully orbited the 23.6 kg (52 lb) Vanguard 3 satellite. That last mission was designated TV-4BU, because it used a remaining test vehicle, which had been upgraded with a new third stage, the Allegheny Ballistics Lab X-248A2 Altair. This more powerful motor enabled the launch of the heavier payload. The combination of the AJ10 liquid engine and X-248 solid motor was also used, under the name Able, as an upper stage combination for Thor and Atlas space launch vehicles.